Aniline

Phototransformation in water

Description of key information

Aniline is photolytically degraded within about 4 to 11 h under spring or summer conditions in the top layer of surface waters

Additional information

“A 10 ^-5M aniline solution was irradiated by May sunlight for 5 hours, and the reaction mixture was analyzed by liquid chromatography. The light conditions were: latitude 40°N, reaction in test tubes which corresponds water surface conditions. A degradation half-life of about one week was found in distilled water. The addition of commercial humic and fulvic acids as well as the use of river water (instead of distilled) lowered the degradation half-life to 4 to 8 hours. As reaction product, azobenzene was detected with a maximum yield of 0.2%, the major products (which are more polar than aniline) were not identified (Zepp et al. 1981).

 

The influence of bicarbonate and carbonate radicals in the presence of H2O2 on the photodegradation of aniline was studied by Larson and Zepp (1988). A 1 μM aniline solution was irradiated with 313 nm light in a merry-go-round photoreactor. The degradation half-lives were 350 min for direct photolysis (0.092 M carbonate, pH 11.6), and 19 min (0.092 M carbonate + 3 mM H2O2) resp. 20 min (0.092 M bicarbonate + 3 mM H2O2) for indirect photolysis. A near-surface half-life of 11 hours (latitude 40°N, summer) was computed based on the test results.

 

Hwang et al. (1987) determined the degradation of aniline in estuarine water (study cited above).

The test flasks were suspended in an outdoor tank through which estuarine water was continuously circulated and water level in the flask was 3 cm below the surface. In experiments that used poisoned water samples (only photolysis takes place) mineralisation half-lives of 103 and 355 days were found for summer resp. winter. The respective half-lives for primary transformation were 36 hours and 125 hours.

 

The available studies show that aniline is photolytically degraded within about 4 to 11 h under spring or summer conditions in the top layer of surface waters. As no quantum yield was determined, a degradation rate cannot be estimated for a total water body (because of dullness and light dispersion, photolysis occurs exclusively near the surface). Therefore a rate constant for the exposure modelling cannot be derived.

 

However, in the experiments of Hwang et al. (1987) photolysis was compared with biodegradation (see above). Under favoured light conditions, photolysis is an important elimination path near the water surface. It was found that, regarding the total water body, biodegradation should be the major elimination pathway in the hydrosphere.”

 

Therefore, for exposure calculations performed in EU-RAR (2004) only biodegradation was considered.

Reference:

ECB (2004). European Union Risk Assessment Report, Aniline, CAS No: 62 -53 - 3, EINECS No: 200 -539 -3, 1st Priority List, Volume 50.